Iron powder for powder metallurgy is used in the production of a sintered part having usually a density of 5.0-7.2 g/cm.sup.3. The part is made by adding and mixing iron powder with Cu powder, graphite powder and the like, shaping into a green compact in a mold, sintering and, if necessary, sizing a sintered body for dimensional correction.
However, the sintered body produced by adding Cu powder, graphite powder or the like to the iron powder is high in the strength, so that it has a drawback that the dimensional correction can not be conducted to a satisfactory extent due to spring-back of the sintered body even if the sizing for dimensional correction is conducted.
As a method of ensuring a desired dimensional accuracy without sizing, therefore, JP-B-56-12304 proposes a technique of enhancing the accuracy of dimensional change by improving particle size distribution of the starting powder, and JP-A-3-142342 proposes a technique of controlling a given size by predicting the dimensional change during sintering from the shape of powder.
However, the iron powder for powder metallurgy is added with Cu powder, graphite powder, lubricant and the like, or mixed for the uniformization of properties in the steps from powder formation to the shaping, or further transferred for replacement with a new vessel, so that the properties such as particle size distribution, shape and the like are apt to be changed at these steps Also, the position change of ingredients due to segregation of Cu powder or graphite powder added to the iron powder occurs and consequently the dimensional accuracy can not necessarily be obtained to a satisfactory extent.